The disclosure relates to machining. More particularly, the disclosure relates to the machining of blade attachment slots in turbomachine disks.
In turbomachines such as gas turbine engines, the blades of fan, compressor, and turbine sections may be secured to separate disks. One attachment means involves providing blade roots having a convoluted section complementary to a convoluted section of slots in the disk periphery. An exemplary configuration involving a convoluted profile that generally increases in transverse dimension from the slot base toward its opening is called a fir tree configuration. A number of methods have been used or proposed for forming the slots. For a long time, the state of the art method for forming the slots involves a broaching process with hundreds of broach cutters in a linear assembly. After an initial machining of a slot precursor, the disk is translated along the broach which may be many tens of meters in length. Cutter profile progressively changes from that of the initial slot precursor to that of the final slot. Such broaching process requires a very substantial capital investment as well as substantial maintenance.
A recently-proposed alternative is found in U.S. Pat. No. 7,007,382 (the '382 patent). In the '382 patent, a small number of rotating abrasive bits are used to transform the precursor slot into the final slot shape. One example involves a first bit having a profile nearly that of the final slot over a depth extending to near the base of the final slot. A second stage involves a bit of essentially the final slot shape over such or slightly different depth. A final pass machines the base of the slot and involves passing a bit rotating about an axis off-normal to a direction of the passing. The off-normal rotation ensures that the bit is continuously moving relative to the disk metal it contacts.